Interfacial water reorganization as a pH-dependent descriptor of the hydrogen evolution rate on platinum electrodes

Hydrogen evolution on platinum is a key reaction for electrocatalysis and sustainable energy storage, yet its pH-dependent kinetics are not fully understood. Here we present a detailed kinetic study of hydrogen adsorption and evolution on Pt(111) in a wide pH range. Electrochemical measurements show that hydrogen adsorption and hydrogen evolution are both slow in alkaline media, consistent with the observation of a shift in the rate-determining step for hydrogen evolution. Adding nickel to the Pt(111) surface lowers the barrier for hydrogen adsorption in alkaline solutions and thereby enhances the hydrogen evolution rate. We explain these observations with a model that highlights the role of the reorganization of interfacial water to accommodate charge transfer through the electric double layer, the energetics of which are controlled by how strongly water interacts with the interfacial field. The model is supported by laser-induced temperature-jump measurements. Our model sheds light on the origin of the slow kinetics for the hydrogen evolution reaction in alkaline media.This work was supported by a TOP grant from the Netherlands Organization for Scientific Research (NWO). Support from MINECO (Spain) through project CTQ2013-44083-P is acknowledged

In situ spectroscopic study of CO\u3csub\u3e2\u3c/sub\u3e electroreduction at copper electrodes in acetonitrile

\u3cp\u3eThe electrochemical conversion of carbon dioxide (CO\u3csub\u3e2\u3c/sub\u3e) into valuable compounds is a promising route toward the valorization of this molecule of high environmental impact. Yet, an industrial process involving CO\u3csub\u3e2\u3c/sub\u3e electroreduction is still far from reality and requires deep and fundamental studies for a further understanding and better development of the process. In this work, we describe in situ spectroelectrochemical studies based on Fourier transform infrared spectroscopy and surface-enhanced Raman spectroscopy of the CO\u3csub\u3e2\u3c/sub\u3e reduction in acetonitrile solutions at copper electrodes. The influence of factors such as the water content and the supporting electrolyte on the reaction products were evaluated and compared to products obtained on metal electrodes other than Cu, such as Pt, Pb, Au, Pd, and Ag. The results show that at Cu electrodes in acetonitrile containing small amounts of water, the main reaction products from CO\u3csub\u3e2\u3c/sub\u3e reduction are carbonate, bicarbonate, and CO. The formation of CO was observed at less-negative potentials than the formation of (bi)carbonates, and the formation of carbonate and bicarbonate species appears to be the result of a reaction with electrochemically generated OH\u3csup\u3e-\u3c/sup\u3e from water reduction. In general, our experiments show the sensitivity of the CO\u3csub\u3e2\u3c/sub\u3e reduction reaction to the presence of water, even at the residual level. (Chemical Equation Presented).\u3c/p\u3

Hydrogen oxidation and hydrogen evolution on a platinum electrode in acetonitrile

\u3cp\u3eThis work discusses the kinetics of the hydrogen oxidation reaction (HOR) and hydrogen evolution reaction (HER) on a polycrystalline platinum electrode in acetonitrile, in presence of two different electrolytes. Our findings indicate the sensitivity of the kinetics of these reactions to the presence of small amounts of water. Insitu FTIR spectroscopy reveals the ion migration owing to the preferential solvation of protons by residual water, whereas surface-enhanced Raman spectroscopy confirms that the water leaves the interface under hydrogen oxidation conditions. These observations imply that the kinetic sensitivity of this electrocatalytic reaction towards the preferential solvation processes presents a serious constraint in the establishment of a reference electrode for nonaqueous solvents based on HOR/HER on platinum, and on the comparison of its catalysis in various nonaqueous solvents.\u3c/p\u3

In Situ Spectroscopic Study of CO₂ Electroreduction at Copper Electrodes in Acetonitrile

The electrochemical conversion of carbon dioxide (CO₂) into valuable compounds is a promising route toward the valorization of this molecule of high environmental impact. Yet, an industrial process involving CO₂ electroreduction is still far from reality and requires deep and fundamental studies for a further understanding and better development of the process. In this work, we describe in situ spectroelectrochemical studies based on Fourier transform infrared spectroscopy and surface-enhanced Raman spectroscopy of the CO₂ reduction in acetonitrile solutions at copper electrodes. The influence of factors such as the water content and the supporting electrolyte on the reaction products were evaluated and compared to products obtained on metal electrodes other than Cu, such as Pt, Pb, Au, Pd, and Ag. The results show that at Cu electrodes in acetonitrile containing small amounts of water, the main reaction products from CO₂ reduction are carbonate, bicarbonate, and CO. The formation of CO was observed at less-negative potentials than the formation of (bi)­carbonates, and the formation of carbonate and bicarbonate species appears to be the result of a reaction with electrochemically generated OH^– from water reduction. In general, our experiments show the sensitivity of the CO₂ reduction reaction to the presence of water, even at the residual level

Lateral Adsorbate Interactions Inhibit HCOO- While Promoting CO Selectivity for CO2 Electrocatalysis on Ag

The analysis presented in this manuscript helps bridge an important fundamental discrepancy between the existing theoretical and experimental knowledge regarding the performance of Ag catalysts for CO2 electrochemical reduction (CO2ER). The results demonstrate how the intermediate species *OCHO is formed readily en-route the HCOO– pathway and plays a decisive role in determining selectivity of a predominantly CO producing catalyst such as Ag. Our theoretical and experimental approach develops a better understanding of the nature of competition as well as the complex interactions between the reaction intermediates leading to CO, HCOO– and H2 during CO2ER.Details of computational and experimental methods are present in the Supporting Information provided. </p

Guidelines for the Rational Design of Ni-Based Double Hydroxide Electrocatalysts for the Oxygen Evolution Reaction

The oxygen evolution reaction (OER) is one of the major bottlenecks hindering the implementation of a global economy based on solar fuels. It is known that Ni-based catalysts exhibit remarkable catalytic activities for the OER in alkaline media. In this joint theoretical–experimental study, we provide a thorough characterization of Ni-based double hydroxides with Cr, Mn, Fe, Co, Cu, and Zn at the atomic scale that not only explains the reasons for their high activity but also provides simple design principles for the enhancement of their electrocatalytic properties. Our approach, based on the local symmetry and composition of the active sites, helps rationalize the effect of dopants on the catalytic activity of Ni­(OH)₂. In particular, NiFe, NiCr, and NiMn double hydroxides (DHs) have superior catalytic activity, which reduce the OER potential to reach 0.5 mA cm^–2 by 230, 190, and 160 mV, respectively, in comparison to IrO₂ nanoparticles, the state-of-the-art benchmarking catalysts, with 90% Faradaic efficiency for O₂ generation. The active species in NiFe and NiMn DHs are iron and manganese, while in NiCr DH, nickel is the active species